Transient resonance Raman spectroscopy and density functional theory investigation of iso-polyhalomethanes containing bromine and/or iodine atoms

We report additional transient resonance Raman spectra and density function al theory computations for the products formed following ultraviolet photoe xcitation of solution phase polyhalomethanes containing bromine and/or iodi ne atoms. We show that the iso-polyhalomethane photoproduct is responsible for the intense transient absorption band observed in the 350-470 nm region after ultraviolet excitation of polyhalomethanes in the solution phase. We examine the trends and correlation in the density functional theory optimi zed geometry and intense electronic absorption transition in the 350-470 nm region for the iso-polyhalomethanes containing bromine and/or iodine atoms . We explore the chemical reactivity of the iso-polyhalomethane species usi ng density functional theory computations for the reaction of iso-CH2Br-Br with ethylene as an example. Our results and comparison with experimental d ata in the literature indicate that the iso-polyhalomethane species is most likely the methylene transfer agent in the cyclopropanation reactions of o lefins using ultraviolet photoexcitation of polyhalomethanes in the solutio n phase. We briefly discuss the possibility that the photochemistry and che mistry of the iso-polyhalomethanes may give significant release of reactive halogens to the atmosphere. (C) 2000 American Institute of Physics. [S0021 - 9606(00)00148-3].